So far, the environmentally destructive mussels have not contaminated McPhee Reservoir, but if they do, the result would be significant infrastructure damage to irrigation and even municipal water systems.
"They clog intake pipes, valves, pump stations, increasing maintenance costs," said Mike Preston, DWCD general manager. "They would kill the fishery."
The district wants to expand prevention measures in cooperation with the Forest Service and CPW to stop an invasion or at least delay it as long as possible.
Quagga and zebra mussels are moving closer to the Four Corners areas. The mussels have wreaked havoc on Lake Mead since 2007, and adult quagga colonies were discovered at Lake Powell in 2014.
Blue Mesa Reservoir, Granby Lake, and Grand Lake had evidence of the quagga larvae, but were de-listed in 2014 after testing negative for five years. Pueblo Reservoir is currently the only Colorado lake testing positive for quagga mussel larvae, and no zebra mussels are known in the state, according to the Department of Natural Resources.
Jim White, an aquatic biologist with CPW, says boat inspections at the McPhee and House Creek boat ramps have been an effective defense, and regular tests are showing up negative. But gaps in coverage are a concern.
The McPhee inspections stations are open from May 1 to October 31, and inspect about 7,000 boats per year. But during the shoulder season and winter off-season, the lake is more vulnerable. Uncontrolled access after inspection hours also allows unchecked boats to enter the water.
Boat owners can help prevent a contamination.
"Clean, drain and dry boats of all water before launching, and after leaving any waterway," White said. "It's a habit that should be automatic. During their early life stage the mussels are microscopic and can live for 27 days in a little water on a boat."
Mussels degrade a lake's native and sport fishery. The species are filter feeders, sucking in phytoplankton and zooplankton that young fish need.
"All that cloudiness in lakes that is what contains the food source for fish," White said. "These things filter out all the fish food, and clear the water."
Additional management could include closing off McPhee boat ramps with gates during the off-season. Locking gates on boat ramps after inspection hours would cause hardships and potentially strand boaters on the lake.
A DWCD report concludes that "more access controls are likely in the future." New rules would involve public input.
The San Juan National Forest manages recreation at McPhee, and CPW contracts out boat inspection duties.
District Ranger Derek Padilla said boat access is supposed to be from either boat ramp to insure inspections. It is not a formalized policy, but it could be if deemed best for protecting the reservoir.
"We get some locals avoiding the inspections by launching over by the cemetery in Dolores," he said. "Visiting boaters utilize the boat ramps and are more likely to have come from an infected area. But to avoid accidental contamination, every boat should go through inspection stations."
Adequate federal and state funding for the boat inspections is uncertain year to year. But political pressure to keep a robust program is critical.
"Investing now in prevention measures saves money in the long run," White says. "At lake Mead, Las Vegas has spent millions of dollars retrofitting intake systems with chlorine flushing units to control the mussels."
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